31 Aug 2009

Solar Power from Space: Moving Beyond Science Fiction

For more than 40 years, scientists have dreamed of collecting the sun’s energy in space and beaming it back to Earth. Now, a host of technological advances, coupled with interest from the U.S. military, may be bringing that vision close to reality.
By michael d. lemonick

Despite the enormous promise of solar power, the drawbacks of the technology remain significant. People need electricity every day, around the clock, but there’s no part of the United States that is cloud-free 365 days a year — and no solar radiation at night. You have to find some way to store the energy for those sunless periods, and there’s not yet a large-scale way to do that.

Moreover, the best locations for solar arrays — the deserts of the American Southwest — are far from the centers of population, so even under the best of circumstances you’d have to send electricity many hundreds of miles through transmission lines that don’t yet exist.

But there is a way to tap into the sun’s energy 24 hours a day, every day of the year, and send it anywhere on the globe: Launch solar panels into space and beam the power back to Earth.

The concept sounds far-fetched and wildly impractical, and when the Pentagon and space enthusiasts began talking about it back in the 1960s and 1970s, it was. Recently, however, the idea of space-based solar power, or SBSP, has begun to look less like science fiction and more like a technology whose time may be coming, with the Pentagon and private companies ramping up efforts to make space-based solar power a reality.

Two years ago, the Pentagon’s National Security Space Office (NSSO) issued a report recommending that the U.S. “begin a coordinated national program to develop SBSP.” A year ago, engineers did a small but successful experiment using some of the technology that will be employed in SBSP, taking energy from solar cells, converting it to microwaves, and then beaming it 92 miles from Maui to the Big Island of Hawaii, where it was converted back into 20 watts worth of electricity.

And last spring, the California-based Solaren Corporation signed a contract with Pacific Gas & Electric (PG&E) to provide 200 megawatts of power — about half the output of an average coal-fired power plant — by 2016 by launching solar arrays into space. Several other companies have announced their intentions to put up solar satellites of their own.

Doubts abound that space-based solar power will come to pass anytime soon, and for good reason: The technology involves launching a series of large satellites into space, using robotic technology to assemble the solar arrays, transmitting the energy 22,000 miles to earth using microwave technology, and then converting that energy to electricity on the ground.

The fact is, however, that all of that is now feasible — if pricey — thanks to technological advances in recent years. These include cheaper and more
The question is whether this engineering feat can be pulled off at a price competitive with terrestrial solar power.
reliable launch technology, lighter and stronger materials for solar stations, significant improvements in the robotic technology needed to assemble the solar arrays, far more efficient solar cells, more precise digital devices to direct that energy accurately to earth, and significantly smaller and more powerful microwave transmitters and receivers.

The big question is whether this engineering feat can be pulled off at a price competitive with terrestrial solar power. So far, the Pentagon’s estimate of what it will cost — $10 billion to put a 10-megawatt experimental solar station in orbit by 2016 — is five times higher than Solaren’s and would produce far less power.

A number of factors are driving the renewed interest in space-based solar power, including the push to cut greenhouse-gas emissions and growing interest from the military. But neither of these forces would mean much if the technology was outrageously expensive or too impractical.

It was a little bit of both when SBSP was first proposed in 1968 by an engineer named Peter Glaser, who worked for the consulting firm Arthur D. Little on a variety of space-related projects. The basic components — solar cells and microwave transmitters and receivers — already existed, and as the Apollo program began to wind down, NASA was trying to figure out what to do next.

In particular, says John Mankins, who became the manager for advanced concepts for NASA during the 1990s, “They were trying to figure out what to do with the space shuttle.” One idea was to begin launching space habitats — to get large numbers of people living and working in space. “These people would need something to do,” says Mankins, “so one idea was that they’d build solar-power satellites.”

Studies showed that it was a feasible, but daunting, proposition. “This was in the days before PCs, microelectronics, robotics,” says Mankins. “The idea of something like the shuttle’s robotic arm was unimaginable. So you’d need these big crews to bolt the things together — and the satellites themselves would have had to be physically enormous. We’d need a new launch system that would dwarf the space shuttle.”

The bottom line, he says, was that it could be done, but it would have cost
At 22,000 miles up, a geostationary satellite is in full sunlight virtually all the time.
the equivalent of a trillion of today’s dollars to get the first kilowatt of power, and it would have taken 20 years. “The National Research Council and the Office of Technology Assessment looked at it,” recalled Mankins. “One of them said, ‘Let’s revisit this in ten years.’ The other said, ‘Let’s never consider this again.’”

In the mid-1990s, NASA did revisit the concept. Under Mankins’ direction, a team of engineers was assembled to see whether advances in technology made space-based solar power more feasible. “The basic answer,” he says, “was ‘yes.’”

In the past decade two other factors have emerged to boost the prospects of SBSP: climate change and interest from the military.

There is a growing recognition that non-carbon energy sources will be crucial if the world is going to avoid the worst effects of climate change. It’s almost inevitable that carbon emissions will end up being taxed one way or another, and when they are, renewables like SBSP will immediately become more competitive economically.

That’s what motivates Solaren and PG&E. Although it is cloaking its work in secrecy, Solaren has said it will cost roughly $2 billion to launch a handful of satellites carrying the equipment that will be robotically assembled into a single, large solar station. One way the company plans to boost efficiency is to use parabolic reflectors to concentrate sunlight onto the solar cells.

“The biggest expense,” says Cal Boerman, Solaren’s director of energy services, “is the cost of getting into space, and we’re convinced we can get the weight down to the point where we can do this with a minimum number of launches.”

As with any SBSP system, the energy will be converted into microwaves
Solaren eventually wants to put in orbit satellites that can generate enough electricity for 1 million homes.
and beamed down to a so-called rectenna — an antenna that “rectifies” the microwaves back into electricity. Solaren’s, to be located near Fresno, Calif., will consist of an array of smaller antennas that will cover about a square kilometer — far less real estate than you’d need if you were using ground-based solar cells to gather an equivalent amount of power.

Because Solaren’s satellite will be in geostationary orbit, the antennas won’t have to track it across the sky; like a satellite TV receiver, they’ll always aim at a fixed point in the sky. At 22,000 miles up, a geostationary satellite is in full sunlight virtually all the time.

As for safety, he says, the fact that the microwaves are spread out over a square kilometer means that they’d be relatively harmless to, say, a flock of birds that happened to fly through them. And if the beam should wander, the satellite will be programmed to scatter it.

Solaren isn’t the only company trying to commercialize SBSP: PowerSat, based in Everett, Wash., has recently filed patents for its own space-power system, which will use an array of hundreds of small satellites linked together rather than one large one. PowerSat says it can reduce some of the high costs of putting the technology in space by using solar energy to power electronic thrusters to maneuver the satellites into orbit. A Swiss company, Space Energy, is also working on SBSP. Solaren is the only one, though, with a contract with a utility. “As we talked to investors,” says Boerman, “they naturally asked, ‘Can you sell it?’”

If this first project works out, Solaren eventually wants to put in orbit satellites that can generate a gigawatt of electricity, enough to power roughly 1 million homes.

Such futuristic schemes have understandably generated a great deal of skepticism. Space experts have been debating the issue online, with some arguing that Solaren’s project will be far more expensive than the company estimates, in part because it could take more than a dozen launches — not just four, as the company stated — to get the solar station into space.

But the military’s interest in SBSP could give a major boost to the technology. According to Marine Corps Lt. Col. Paul Damphousse, Chief of Advanced Concepts for the National Security Space Office, the military is interested in SBSP for two main reasons.

The first, he said, is that “we’re obviously interested in energy security, and
By being an early customer, the government can rapidly accelerate development of the technology.
we’re also interested in weaning ourselves off fossil fuels because climate change could pose national security risks.” But there would also be a tactical advantage to space-based solar, Damphousse noted. When the military is operating in remote regions of countries like Iraq or Afghanistan, it uses diesel generators to supply forward bases with power.

“We have a significant footprint getting energy in,” says Damphousse, noting the need for frequent convoys of oil tankers, the soldiers to protect them, and air support — all of which is expensive and dangerous.

Being able to tap into power beamed directly down from space would clearly have a lot of appeal, says Damphousse, even if it were relatively costly. And it’s not just useful for the battlefield, he says, but also for areas affected by natural disasters, such as Hurricane Katrina.

For those reasons, Damphousse supports the idea of coordinated studies by the Pentagon and other agencies — such as NASA and the Department of Energy — that would have a stake in space-based power.

“We might, for example, do some experiments on the International Space Station, which is already up there and generating 110 kilowatts of power from its own solar cells,” he says, “rather than having to send up a dedicated test satellite.”

Such cooperation might appeal to NASA. “I suspect that NASA will start working on energy and on more advanced technology and less on, ‘Let’s get to the moon by 2018,’” says Mankins.

By undertaking some of the research and being an early customer for SBSP, the government could rapidly accelerate development of the technology. Historians of aviation agree that the government’s decision to back air mail played a major role in developing the aircraft industry, leading to technological innovations and economies of scale. The same phenomenon could take an emerging but outlandish-sounding technology and push it into the energy mainstream.


Michael D. Lemonick is the senior writer at Climate Central, a nonpartisan organization whose mission is to communicate climate science to the public. Prior to joining Climate Central, he was a senior writer at Time magazine, where he covered science and the environment for more than 20 years. He has also written four books on astronomical topics and has taught science journalism at Princeton University for the past decade. In other articles for Yale Environment 360, Lemonick wrote about new evidence that makes the 2007 report by the Intergovernmental Panel on Climate Change already outdated and the disturbing picture painted by a recent report on climate change in the United States.

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It would certainly be as feasible and more profitable than having a base built on the Moon.

As NASA is assessing anew its priority, the Ares 5 rocket could be manufactured first for the purpose of launching the SBSP satellite(s) in synchronous orbit, and later, this powerful rocket could be used for the moon project, whatever it may be. This would kill two birds with one stone.

Moreover, it would keep a long term job for NASA engineers and subcontractors teams.
Posted by François Le Roy on 01 Sep 2009

200 megawatts in a "handful" of microwave beams from space going through the entire atmosphere? Woe betide any hapless migratory bird or plane to pass through a 10-megawatt maser beam! Instant atomization would be the consequence. At these power levels blooming from maser absorption by water vapor would create a channel of superheated air. Convection could establish a permanent strong updraft vortex - an anchored tornado. The possibility of creating an electrolaser effect between the ground and the stratosphere is also considerable. What fun!
Posted by Tom Davidson on 01 Sep 2009

Tom, that would be applicable if we had a concentrated beam. This is over a square kilometer. 10 MW / 1 million square meters = 10 W/m^2. That's a bright sun beam, not anything to be afraid of. The updraft would be greater if we had a parking lot. It's a valid point that has already been addressed.

I have to admit, when I first saw this in Sim City 2000 (yes, the video game), I thought that it would never work. I hope that I was wrong.
Posted by Ben on 01 Sep 2009

Three questions to the author:

1. Compared with thousand miles of transmission line from desert areas of the US to the eastern coast, a transmission line tens of thousand miles from the space to the surface of the earth is really more cost effective and efficient on energy conversion?

2. Will those extra solar energy accelerate Global Warming? I am not expert, but according to the rule of energy constant and this brilliant idea, how will the earth deal with those extra heat?

3. Do you ever considered the disposal of these benign space solar panels? If it is only for military purpose, there probably won't be a huge impact on the space, but if it is promoted as a business, who is going to in charge of waste treatment of these equipments?

Posted by Feng Wang on 02 Sep 2009

Solaren and PG&E deal is 100% scam.
Posted by Hua Zhang on 04 Sep 2009

Joe Romm makes a pretty good case that the PG&E deal is a scam, or at least isn't going to work for several reasons that are valid in the short term. See

In the long term there's nothing inherently speculative about the idea. All the necessary technologies exist, even the ability to manufacture carbon-neutral rocket fuel to launch pieces of the systems.

The military application for space-based power is to provide reliable power to remote locations. It makes a poor weapon because it's so big, expensive and easy to attack. Any harm it could do would be done far more cheaply and easily with missiles or bombs.

We need to recognize that eliminating fossil fuels is going to be very expensive, take decades, and in the case of wind and ground-based Solar require thousands of square miles of area for collectors and hundreds of thousands of miles of new transmission lines. Nuclear at least has the advantage of compactness.

Space-based Solar power would make a negligible contribution to global warming. If it provided all of humanity's energy it would add less than 0.1% to the energy the Earth already receives from the Sun.

Since radiated thermal power increases with the fourth power of temperature the Earth's temperature would be multiplied by less than the fourth root of 1.001, or 1.00025. The greenhouse effect from CO2 released by fossil fuels has a far larger effect because it reduces Earth's emissivity; already it has increased average temperature by 0.3'C, or 1.001, and rising.
Posted by richard schumacher on 09 Sep 2009

See the URL for a detailed response. The basic problem as shown is that cost will almost certainly not become practical for a complete Earth based launch version. In-situ materials can possibly change that outcome, but the up-fromt commitment would have to be very large, and it would only work for very large scale systems.
Posted by Leonard Weinstein on 12 Sep 2009

Interesting to see how the above comments seem to take for granted that we need to substitute polluting energy for clean (here solar) energy. My take on this would be that solar power from space would rather be used to add to the supply of energy, and not necessarily to replace coal power plants as such. If coal power plants are still profitable, be there space solar power available or not, there will still be coal power plants, no? I would tend to believe that demand for coal power will no suddenly shrink as soon as new cleaner techs will be developed, given that economic growth will always demand more energy to support it...

The problem might thus lie elsewhere and energy substitution might not provide a real solution after all - i.e. growth itself might the problem. I know it's hard to question economic growth. Maybe because it brings questions of distribution and equity, much harder to solve than sending stuff in orbit to generate more energy.
Posted by jps on 04 Oct 2009

We have only begun to really look at SBSP. The lack of funding is a major issue - however, that should not stop us from looking at this in greater detail. I just finished an article (38 pages) which shows thats SBSP is economical. However, it doesn't look like the normal concepts you may have seen. It uses a thermal system rather than the solar cells you see in the concepts. It also uses a different orbit.

If you would like a copy just send me an e-mail at

Posted by Royce on 06 Oct 2009

The economics of SBSP can be improved if it is used in combination with solar arrays on the surface. The latter are far cheaper when the sun is well above the local horizon, but produce no power at night, necessitating expensive energy storage, or expensive transmission over long distances. This problem can be mitigated by use of SPSP arrays that can be switched from one rectenna array to another, providing power when and where it is needed to complement the ground-based system. The switching can be diurnal or seasonal, or a combination of both. Ground-based solar arrays can be co-located with rectenna arrays, to share the same real estate and the transmission lines to user sites, or sited separately if this is more advantageous.
Posted by HOWARD ROBBINS on 17 Oct 2009

As far as I am concerned we need to do what we can to further solar power by any means and by as much as possible. We can sit here and talk about how much money it will cost for us to put satellites in space in order to collect the energy then to beam it down to earth. Or if it is economically feasible and blah, blah.

Look, the truth of the matter is, yes it will cost us money and if we wait longer there will be better technology and it will be cheaper. But money doesn't mean a thing if you can't breath, right.

Posted by Eli Wagar on 24 Nov 2009

It's a thought provoking idea, although the economics of space transportation don't make this idea work yet.

They say the total weight of the space system is around 15000 metric tonnes. At launch costs of 10000 USD per kilogram, the cost of a 1 GW space system would be 150 billion just in launch costs! However, launch costs may very well come down a lot. At 1000 USD per kilogram, it's 15 billion, very close to being competitive. But still not 6.5 cents per kWh, and that doesn't include the rest of the system, such as the terrestrial receiver equipment. Not to mention the costs of the solar cells and laser/transmitting device for beaming the energy to earth. Can't use GaAs because the energy per area collected per year isn't big enough to justify the extreme cost. It would be anologous to having a 10x terrestrial (eg desert) concentrating GaAs cell. They cost like 100 USD per Watt, and 10x concentration (very roughly equivalent to energy gain in space) makes it 10 USD per Watt. Too high, with 15 USD per Watt lauch cost under the optimistic launch cost projection, it's 25 USD and that still doesn't include the terrestrial receiver.

New PV technology, such as infrared nano antenna's, could change this picture, so it's a good thing they're keeping an open mind on the subject and have gotten funding.

Basically, it's a long shot, even under very optimistic assumptions of future economics and technology development. At least we can't blame them for lack of ambition!

I think that the energy return on energy invested also has to be calculated. Launching things into space is extremely energy intensive, so we need to see some calculations to see if this is even energy positive in the first place.

Posted by Acompanhantes on 15 Dec 2009

I think even if the cost is higher we should definitely follow this direction and promote this new technology and develop it further. As the demand for electricity is growing fast, we need new solutions that can be used on big scales. Then prices will drop automatically.
We need to replace coal power plants, even if they are more economically, pollution needs to be avoided in any way, no matter if your believe in climate change or not. Our ultimate goal should be to run on 100% renewable energy sources but there is still a very long way to go.

Posted by Chris on 18 Jan 2010

One year later the science behind this article remains a strong possibility, but seems to be taking a back seat to the newer method recently profiled on 60 minutes.
I just don't imagine that the high cost and roi on this project is going to entice too much private investment.
Posted by jeremy e on 27 May 2010

I'm coming to this article quite awhile after it was written -- November 1, 2010 -- but I found it interesting anyway, as I've been intrigued by the idea of SBSP for many years, though I realized from the start that there were enormous hurdles to ever make it practical.

I don't how much danger a microwave beam would or would not present, but I do remember reading that the Japanese were looking into the possibility of placing the rectenna far out in the ocean. If such a beam does indeed present any sort of danger to aircraft or ships (including interfering with their communication and navigation equipment maybe?), a small no-go/no-fly zone could be established around such a floating installation. But I do have some doubt that any threat really exists.

Running an experiment on the ISS strikes me as a very good idea, since it's already in place and will be for some years to come (barring any major accident, of course).

I hope this becomes a practical alternative to fill at least some of our energy needs.

Posted by Mekhong Kurt on 01 Nov 2010

I really hope solar makes it. It seems the forgotten aspect of climate change mitigation at least in Australia.

Posted by Brendan on 15 Jun 2011



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